CN104410053B - DC power transmission system traveling wave protection method - Google Patents

Abstract

The invention relates to a traveling wave protection method for a direct current transmission system, which belongs to the technical field of ultra-high voltage direct current transmission. The present invention collects the line current and voltage of the station, calculates the polar wave P _I , and then analyzes the polar wave P _I using S-transformation to obtain the time-frequency distribution characteristics of the polar wave S-transformation modulus, and the moment with the largest mutation is The moment when the fault occurs; and then process it according to the protection criterion and protection action strategy, the criterion is P _set ≥ K _rel · P _max , the reliability coefficient K _rel > 1, and P _max is the polar wave S transformation among all external faults and disturbances The maximum value of the modulus, and satisfying that the pole wave setting value calculated by the above formula is obviously smaller than the first wave peak value of the fault polar wave S transformation modulus in the area, so as to ensure that the protection will not malfunction when the fault is outside the area, It can also ensure the reliable operation of the protection in case of faults in the zone. The method proposed by the invention can quickly and accurately judge the fault, and avoid the risk caused by the misoperation of the line traveling wave protection.

Description

A traveling wave protection method for direct current transmission system

technical field

The invention relates to a traveling wave protection method for a direct current transmission system, which belongs to the technical field of ultra-high voltage direct current transmission.

Background technique

After a fault occurs on a HVDC transmission line, its voltage and current usually contain a wealth of non-power frequency transient components, and the fault component varies with different fault conditions such as fault time, fault location, transition resistance, and system operating conditions. Variety. Therefore, effective analysis of fault transient signals and extraction of corresponding fault feature information are of great significance for rapid action of system protection, accurate identification of fault types, and rapid location of fault points.

Power system transient signals are typical non-stationary signals. In traditional signal processing, Fourier transform establishes the connection between the signal time domain and frequency domain, so it becomes the most common and direct method for analyzing and processing signals. With the development of computer technology, software implementation of fast Fourier transform has greatly improved the calculation speed, but for non-stationary transient signal, Fourier transform can only be carried out in a limited interval, which inevitably exists due to time The energy leakage caused by domain truncation may cause large errors in the amplitude, phase and frequency of the spectrum, which greatly limits its application in power system transient signal processing. For this reason, such as ratio correction method, energy center of gravity correction method, etc. are used to improve the traditional Fourier transform, so that the analysis results have better time resolution and precision. This type is suitable for time domain signals and frequency domain signals. The transformation of the signal is called time-frequency analysis. The main problem of traditional traveling wave protection is that it cannot accurately grasp the transient information of line faults, so the reliability, quickness, accuracy and anti-interference ability of its operation are greatly affected.

Contents of the invention

The purpose of the present invention is to provide a traveling wave protection method for a direct current transmission system to solve the problem that the traditional traveling wave protection cannot accurately grasp fault information.

In order to solve the above technical problems, the present invention provides a traveling wave protection method for a direct current transmission system. The protection method includes the following steps:

1) Collect the voltage signal and current signal of the DC transmission system, and calculate the line polar wave according to the collected voltage and current signal and the line wave impedance;

2) S-transform the polar wave of the line to obtain the time-frequency distribution characteristics of the modulus value of the polar wave S-transform before and after the fault;

3) Calculate the S-transform frequency of the polar wave as the modulus of the polar wave protection judgment frequency band, and use it as Pset;

4). Calculate the maximum value P _max of the polar wave S-transform modulus among all external faults and disturbances, and determine whether to take protective action on traveling waves according to the relationship between P _set and P _max .

The polar wave calculation formula in the step 2) is:

P _I (t) = Z _p ·i(t)-u(t)

Among them, Z _p is the polar wave impedance, i(t) is the collected current signal, and u(t) is the collected voltage signal.

The protection criterion in the step 4) is:

P _set ≥ K _rel P _max

K _rel is the reliability coefficient, K _rel >1; P _max is the maximum value of polar wave S transformation modulus among all external faults and disturbances, if the above formula is true, the traveling wave protection will operate.

The P _max is 5-6, and the protection judgment frequency band of the polar wave is the 59th harmonic or the 61st harmonic of the S-transform.

The beneficial effects of the present invention are: the present invention collects the line current and voltage of this station, calculates polar wave _PI , then adopts S to analyze polar wave _PI , obtains the time-frequency distribution characteristic of polar wave S transform modulus, The time when the mutation is the largest is the time when the fault occurs; then it is processed according to the protection criterion and protection action strategy, the criterion is P _set > K _rel P _max , the reliability coefficient K _rel > 1, and P _max is the The maximum value of the polar wave S-transformation modulus in the disturbance, and satisfying that the polar wave setting value calculated by the above formula is obviously smaller than the first peak value of the polar wave S-transformation modulus of the fault in the area, so as to ensure that the faults outside the area The time protection will not malfunction, and it can ensure the reliable action of the protection when the fault occurs in the zone. The method proposed by the invention can quickly and accurately judge the fault, and avoid the risk caused by the misoperation of the line traveling wave protection.

Description of drawings

Fig. 1 is the flowchart of the traveling wave protection method of DC transmission system of the present invention;

Fig. 2 is a program flow chart of fault feature extraction for traveling wave protection.

detailed description

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

1. First collect the line current and voltage of the station, and calculate the polar wave according to the relationship between the sampled value of the current and voltage signal and the polar wave impedance of the DC line P _I (t)=Z _p i(t)-u(t) P _I .

2. Analyze the polar wave P _I by using S transform, and obtain the time-frequency distribution characteristics of the modulus value of the polar wave S transform before and after the fault. The moment when the mutation is the largest is the time when the fault occurs. The calculated S transform frequency of the polar wave is 3000HZ The modulus Ap of is taken as P _set .

The pole wave protection judgment frequency band is the signal whose frequency distribution is 2950-3050 Hz after the fault pole wave S transformation, and generally takes the 3000 Hz signal.

3. Calculate the maximum value P _max of the polar wave S-transform modulus among all external faults and disturbances, and judge whether P _set is greater than K _rel ·P _max , that is, whether the following formula holds.

P _set ≥ K _rel P _max

Among them, K _rel is the reliability coefficient, which can be 1.1~1.2. According to the simulation results, P _max is 5~6, which can take into account the sensitivity and reliability of the protection. The protection judgment frequency band of the polar wave is the 59th harmonic or 61st harmonic of the S transformation. harmonic.

4. If the above formula is established, the traveling wave protection outlet will act, and a line fault restart command will be issued to carry out the DC system fault recovery sequence.

Detect the head of the traveling wave and judge the protection of the traveling wave. The frequency band for the protection judgment of the polar wave is the signal with a frequency distribution of 2950-3050 Hz after the S-transformation of the fault polar wave. Generally, the signal of 3000 Hz is taken. The criterion is P _set ≥ K _rel · P _max , which is reliable The coefficient K _rel > 1, P _max is the maximum value of the polar wave S-transformation modulus of all external faults and disturbances, and the polar wave setting value calculated by the above formula is obviously smaller than the internal fault polar wave S-transformation modulus In this way, it can not only ensure that the protection will not malfunction when there is an external fault, but also ensure that the protection will operate reliably when there is an internal fault. K _rel > 1 can be 1.1~1.2, and P _max can be 5~6.

The present invention can be realized by an embedded industrial control platform or a PC device, and these two devices are commonly used devices in the field of high-voltage direct current transmission. The protection device first collects the line voltage and current, and generates polar wave signals, and then extracts the fault features and judges the fault time according to Figure 1 and Figure 2.

Claims (4)

1. a kind of DC transmission system traveling-wave protection method, it is characterised in that the guard method is comprised the following steps：

1) voltage signal and current signal of DC transmission system are gathered, according to the voltage and current signal for collecting and circuit wave resistance Anti- calculating circuit pole ripple；

2) S-transformation is carried out to circuit pole ripple, obtains time-frequency distributions characteristic of the modulus value of pole ripple S-transformation before and after failure；

3) the S-transformation frequency for calculating pole ripple is the modulus value that pole ripple protection judges frequency range, and as P_set；

4). calculate the maximum P of all external area errors and the pole ripple S-transformation modulus value in the middle of disturbance_max, according to P_setWith P_maxPass System determines whether to carry out protection act to traveling wave.

2. DC transmission system traveling-wave protection method according to claim 1, it is characterised in that the step 2) in pole Ripple computing formula is：

P_I(t)=Z_p·i(t)-u(t)

Wherein P_IT () is pole ripple, Z_pFor pole natural impedance, i (t) is the current signal of collection, and u (t) is the voltage signal of collection.

3. DC transmission system traveling-wave protection method according to claim 2, it is characterised in that the step 4) in guarantor Protecting criterion is：

P_set≥K_rel·P_max

K_relFor safety factor, K_rel＞ 1；P_maxFor all external area errors and disturbance in the middle of pole ripple S-transformation modulus value maximum, If above formula is set up, traveling-wave protection action.

4. DC transmission system traveling-wave protection method according to claim 3, it is characterised in that the P_max5～6 are taken, pole The protection of ripple judges frequency range for 59 subharmonic or 61 subharmonic of S-transformation.